Because this corresponds to the highest gear (in old times a.k.a. direct gear) and cruising speed. The max. power test is best done by achieving max. speed. Doing it at lower speeds and gears opens to slipping between wheel and roller, so the measerement would be impaired and/or results unreliable.

Because that will give you your most accurate readings. A lower gear will multiply the horsepower reading because it takes less power to turn the drive train in a lower gear. if you did it in overdrive it would decrease the power reading because overdrive is designed for fuel economy, not power. Hope this helps.

I would presume it's a benchmark. If everybody did different gear ratio's then you wouldn't have a constant and reliable means to collect data to compare to.

In other words if its a 4 speed you want it in 4th. If its a automatic you want it in third. No over drive. That would lug the engine and give inaccurate results. One to one ratio will be actual HP / torque.

so torque is not amplified/multiplied through gear reduction.

I tried to research this on the internet, but couldn't find the actual reason for why this is done.

basically, when a car or a bike is put on a dyno test, why should the test

should be performed in a gear with a ratio of 1:1 or as near as possible to

this ratio?

Any answers related to this would be appreciated